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5-Minute Foam Factory 

Make] Projects 

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build, hack, tweak, share, discover,- 

5-Minute Foam Factory 

Written By: Bob Knetzger 


Alligator test leads (2) 

Drill (1) 

Hacksaw (1) 

Hammer (1) 

Handsaw (1) 

Multimeter (1) 
with Q setting 

Screwdriver (1) 
Tape measure (1) 


Screws (1) 

Nails (1) 

Pegboard (1) 

Lumber (1) 

or any dimensional lumber 

EPS foam material (1) 

Sure, you can buy it at a craft store, but 


why not get creative and recycle? 

Super glue (1) 

or any cyanoacrylate glue 

Bolt (1) 

any size 

Nuts (4) 

same size as bolt 

Paper or cardboard (1) 
for making templates 


Model train transformer (1) 

One with variable DC control is ideal. 


with a resistance of 70. per foot. Get it at 
a hobby store or online. 


© Make Projects 

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5-Minute Foam Factory 

What keeps your coffee warm but also rides the cold Pacific surf? What's in the Rock and 
Roll Hall of Fame but makes an annoying, squeaky sound? Even though it's banned in over 
100 cities, you can find it just about everywhere. What is it? It's expanded polystyrene 
(EPS) foam. 

Styrofoam is a great insulator (for hot drink cups and wall insulation), lightweight and stiff, 
and impervious to water (great for surfboards). Unfortunately, it's also impractical to recycle 
and can be an unsightly part of the waste stream. Our landfills and waterways are filling up 
with discarded coffee cups, store meat trays, and take-out packaging. 

With this easy hot-wire foam cutter, you can reuse this leftover EPS foam to create 
treasures from trash! 

Once you've mastered the basic foam cutting techniques, you can create a double-cut, 3D 
teddy bear shape, spin a compound-curve cone, and cut a stack of foam sheets to make a 
blizzard of snowflakes. 

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5-Minute Foam Factory 

Step 1 — Gather your materials. 


• Scrounge your workshop for scrap materials to build the cutter. None of the dimensions 
are critical, so feel free to adapt the sizes shown here to use what you've got. 

• When heated, EPS can produce benzene, and when burned, it gives off other 
noxious fumes. So always use your hot- wire cutter in a very well-ventilated area! 

• Use the train transformer's speed control to set the wire temperature: just warm enough 
to cut the foam. Never cut with a red-hot, smoking wire! 

• Foam made by Woodland Scenics is specially manufactured so that it doesn't give off 
harmful fumes when cut with a hot wire. Get it where model train supplies are sold or at 

© Make Projects 

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5-Minute Foam Factory 

Step 2 — Make the cutter base. 

• Measure and cut the pegboard to make a tabletop. Mine is 18"x18". Then measure and cut 
2 pieces of 2x4 to make leg rails. 

• Use screws to attach the top to the rails. Then place a Vi" drill bit through the outermost 
middle pegboard hole above one of the 2x4s and drill all the way through the rail. This will 
be the hole that the rod fits into. 

• Wear eye protection when using all tools, and to be extra safe, wear gloves when 
cutting with the hot wire. You don't want to touch it — it's over 200° 


Step 3 — Bend and insert the rod. 

Cut the aluminum rod to 21" in length. Mark off 12" and bend the rod about 90°. After 
bending the rod, insert the short leg into the hole you drilled in Step 1b and align as shown 
here. Mark the closest pegboard hole beneath a point 1" or so from the tip of the rod. Then 
mark the top surface of the rod directly above the marked hole. 

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5-Minute Foam Factory 

Step 4 

• Use the hacksaw to make a shallow notch across the top of the rod where it's marked. 

• Insert the rod and drill a small 5" pilot hole through the rail and into and through the 
aluminum rod. Drive a nail into the hole and through the rod. This prevents the rod from 
swiveling in its hole as you cut in different directions. 

Step 5 — Make and attach the cutting wire. 

• Thread 2 nuts onto the bolt. Wrap, then tie the nichrome wire around the bolt, and add the 
remaining 2 nuts. Tighten the 2 nuts in the middle to pinch the wire. 

• Align the nuts so that they all lie flat. Put a drop of super glue on them to lock them tight. 

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5-Minute Foam Factory 

Step 6 

• Thread the nichrome wire through the marked hole in the pegboard (from Step 2a) and pull 
it up vertically. Press the tip of the rod down slightly and hold it there. (You want a little 
springy tension to keep the wire taut.) At the same time, make a loop in the wire so that 
the tip of the loop just reaches the deflected rod. Hold that loop and tie it off in a simple 
overhand knot. 

• As you press the rod down, slip the loop over the rod and into the notch. Let go. The gentle 
spring force of the rod should make the wire taut. If it's too loose, shorten the wire by tying 
another knot. Trim any stray ends. 

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5-Minute Foam Factory 

Step 7 — Check the circuit. 

• Remember your high school 
physics about electricity? Voltage 
equals current times resistance: V 
= I*R 

• You can measure the resistance of 
the wire with a voltmeter: set it to 
"ohms" and measure the wire by 
placing 1 probe at each end point. 
My wire measures 7Q. My 
transformer puts out 12 volts DC. 
Plugging that into the formula 

• 12 = I *7or 12/7= I. So I = 

• So the current needed is just under 
2 amps. My train transformer is 
rated at 2 amps, so that's good, at 
least for short time periods. The 
resistance of the wire will change 
at various temperatures, so the 
current drawn will vary. Many train 
transformers have a built-in 
thermal breaker — if they get too 
warm, they'll shut off. If that 
happens, unplug the transformer 
and let it cool down. It should work 
again later. 

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5-Minute Foam Factory 

Step 8 — Power up! 

• Use the alligator clip leads to attach the train transformer. First, unplug the transformer. 
Connect the first lead from one side of the regulated DC contacts to the bolt underneath 
the table. Connect 1 clip of the second lead to the remaining DC voltage contact on the 
transformer. Make sure the variable control is at its lowest setting, then plug in the 

• Ready to test it? Finally, connect the last alligator clip to the base of the rod. You've 
created a circuit that sends current through the wire. Adjust the transformer's control so 
that the wire gets warm — not glowing red-hot. No heat? Check your connections and 
make sure the clips aren't touching each other at the transformer. 

• Test your cutter with a scrap of foam. Place the foam on the table surface and gently slide 
it into the hot wire — it should cut easily with just the slightest pressure. Adjust the voltage 
if needed. Don't press too hard, or you'll pull the wire into an arc and your cuts will be 
curved instead of straight. 

• Use that last connection to the rod as your on/off switch. You can see when it's connected 
and that the hot wire is "on." 

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5-Minute Foam Factory 

Step 9 — Start cutting! 

• You can cut free-form shapes easily — just keep the foam moving at a smooth, constant 
speed. You'll notice that the slightest wiggle in your movements will result in a wavy or 
ridged part! Here are a few tricks for easy cutting and perfect parts. 

• For straight cuts, make a guide from a piece of 1 x2 lumber and some Vi" dowels. Drill 2 
holes on 1" centers and slip in pieces of dowel. Plug these dowel pins into the pegboard 
and you've got an adjustable fence for smooth, straight cuts. 

• Position the fence close to the wire to cut thin strips or position the fence farther away 
to make wide cuts and to square up blocks. For size adjustments of less than 1", 
remove 1 of the dowel pins, and use just 1 pin as a pivot. Swivel the fence around the 
pin to adjust the angle until the distance between the wire and the fence is just right. 
Place a second long dowel pin behind the fence at the closest pegboard hole. Fast and 

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5-Minute Foam Factory 

Step 10 

• For circles, make a circle cutter guide out of a dowel and a nail. Cut a dowel to a length so 
that when inserted into a pegboard hole, it's flush with the tabletop. Drill a 5" pilot hole into 
the end of the dowel and insert a small nail — head first. Tap it in with a hammer. Now you 
have a dowel with a pointy pin sticking out — be careful! 

• Place the dowel in any pegboard hole. The distance from the wire to the pin will be the 
radius of your circular cut. Energize the wire. Slide a piece of foam into the wire and 
impale the foam on the pin. As you spin the foam around on the pin, you'll cut a perfect 
circle. Turn off the wire and remove your part. 

Step 11 

• You're not limited to 90° cuts. For angled cuts build an elevated and angled wedge to 
make beveled cuts! Make a wedge of the desired angle and nail it to a block with dowels 
on the bottom. 

• Plug the wedge into the pegboard and slide the foam to make your angle cut! 

© Make Projects 

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5-Minute Foam Factory 

For more super cool techniques for cutting hyperbolic, toroidal, and conic shapes, as well as 
how to use templates, go to . 

This project first appeared in MAKE Volume 16 , page 114. 

This document was last generated on 201 3-01 -28 1 2:39:32 PM. 

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